Conference Proceedings Paper
Challenges in New Containment Boundary for Refurbishing Unit(s) at a Multi-Unit CANDU® Station
9th International Conference on CANDU® Maintenance - 2011 December 04-06
J. Mike Francisco (AMEC NSS)
Michelle Poei (Bruce Power)
Cecilia Mucio (AMEC NSS)
Vinod Chugh (AMEC NSS)
As part of Unit (s) refurbishment program in a multi-unit CANDU station, a horizontal isolation bulkhead is installed at the bottom of the reactor vault, along with other isolation provisions. This is required to isolate each unit from the Fuelling Machine (F/M) duct and hence operating units to establish a new containment boundary. The isolation bulkhead is a single boundary component and is considered to be a ‘significant modification to the containment boundary’. This factor, along with its complexity and other component isolations make it impractical to test the bulkhead separately. As a result, proof and leakage rate tests of the modified containment boundary must be performed, by testing the isolated Units, in accordance with the requirements of CSA Standard N287.6.
The other isolation provisions include the seal at the bottom of the shield tank and additional process system penetrations from the reactor vault to the FM duct which has to be sealed. These sealed system penetrations along with the shield tank seal will be tested with the rest of the containment boundary for leak tightness and integrity.
Once the bulkhead has been successfully tested and established as the new containment boundary, the isolated Unit(s) can be opened so that refurbishment of the various components, systems in the refurbishment Unit (s) can be started.
The principle objective of this testing program is to demonstrate that the containment isolation bulkheads and other isolation provisions as installed in the isolated Units will make an acceptable containment boundary to isolate these units from the effects of a LOCA or other transients in one of the operating units. The testing which will be performed on the isolated Units will also provide test data to benchmark the leakage characteristic of the isolated Units separate from the operating units and to identify if any new repair or refurbishment efforts will be required before restart.
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